Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
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On average, the 3-year <strong>rotations</strong> had highest total weed seed <strong>de</strong>nsities and species diversities,<br />
probably due to the strongly reduced herbici<strong>de</strong> inputs and diversified <strong>crop</strong> sowing dates in this<br />
system, while the plant communities in continuous corn had lowest species diversity and<br />
evenness (high abundances prevalence of single weed species such as C. album) and grasses<br />
were more frequent in the <strong>rotations</strong> including hay <strong>crop</strong>s. Moreover, several interactions<br />
between the rotation and tillage treatments were significant.<br />
Bellin<strong>de</strong>r et al. (2004) compared the weed seed banks before and after four 2-year <strong>crop</strong><br />
<strong>rotations</strong> including alfalfa, clover (Trifolium pratense L.), rye (Secale cereale L.), and sweet<br />
corn (Zea mays L. var. rugosa Bonaf.) <strong>with</strong> a rye cover <strong>crop</strong> at three sites in New York, USA.<br />
Weed seed banks increased in all four systems. Increases were highest in rye, while seed bank<br />
<strong>de</strong>nsities did not differ between the two mown forage <strong>crop</strong>s and corn, although pre- and post<br />
emergence herbici<strong>de</strong>s and soil tillage (disking) was used only in corn.<br />
Teasdale et al. (2004) and Cavigelli et al. (2008) compared the weed seed banks during 6<br />
years between three <strong>crop</strong> <strong>rotations</strong>: (i) a 2-year corn (Zea mays L.)–soybean [Glycine max (L.)<br />
Merr.] rotation, (ii) a 3-year corn–soybean–wheat (Triticum aestivum L.) rotation, and (iii) a<br />
4+-year corn–soybean–wheat–red clover + cocksfoot (Trifolium pratense L. + Dactylis<br />
glomerata L.) hay rotation. Annual dicotyledonous species including Amaranthus hybridus L.<br />
and C. album, the most harmful weeds in these systems, showed reduced seed bank <strong>de</strong>nsities<br />
after the hay phase while some annual grasses showed the opposite effect. The weed<br />
suppressive effects were strongest when the 4-year <strong>rotations</strong> started <strong>with</strong> hay <strong>crop</strong>s.<br />
Stevenson et al. (1997; , 1998) found greater weed species diversity in a barley/forage rotation<br />
compared to a barley monoculture. The barley-forage rotation showed increase in barley dry<br />
weight seed yield (+ 29% and + 26% compared to the monoculture) in all years except one,<br />
<strong>de</strong>spite greater weed pressure in the barley-forage rotation, suggesting benefits of forages to<br />
subsequent annual <strong>crop</strong>s.<br />
Albrecht (2005) analyzed the weed seed banks during 8 years on a farm recently converted to<br />
organic practices in Bavaria, Germany. On average, rotated grass-clover forage <strong>crop</strong>s<br />
(un<strong>de</strong>rsown in winter cereals, lasting 1.5 years) reduced the seed bank <strong>de</strong>nsity by 39%, winter<br />
cereals (wheat or rye, Secale cereale L.), sunflowers ( Helianthus annuus L.) and lupins<br />
(Lupinus albus L.) increased it by 30-40% per year and potatoes (Solanum tuberosum L.) and<br />
sown fallows caused no significant changes.<br />
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